I recommend asking in the Mk6/Golf R forums. I have no personal experience with these but, I know in the Mk4 quite a wide range of offsets and tire widths are do-able regardless of what came stock on the car.
Also, most would say a 235 is too wide for a winter tire but, I've run them for 3 years without issue. Sure, it's not ideal for real winter weather but, it all depends on what kind of winter weather you typically experience. If you see deep snow, then you'd want something narrower. If slushy stuff or brief sleet/icing/lighter snow is more typical, then it doesn't matter so much.